The Compendium of Caraka 8.1.56

8.1.56

na yāti bastirna sukhaṃ nireti doṣāvṛto 'alpo yadi vā 'alpavīryaḥ/
prāpte tu varconilamūtravege vāte+&ativṛddhe 'alpabale gude vā//

an enema does not pass in nor does it come out easily, if it is enveloped by doṣas, small in quantity, or of low potency;
when an urge for stool, flatus, or urine has arrived, when vāta is exceedingly aggravated, or when the rectum is weak,